INFLUENCE OF LARGE WOODY DEBRIS ON RETENTION, IMMIGRATION, AND GROWTHOF COASTAL CUTTHROAT TROUT (ONCORHYNCHUS CLARKI CLARKI) IN STREAM POOLS

Over 4 months and about 1 year, coastal cutthroat trout (Oncorhynchus clarki clarki) greater than or equal to age-1 in Little Jones Creek, C alifornia, remained at similar rates in pools with and without large w oody debris. This result was based on attempts in July and November 19 95 to collect and tag all fish in 22 pools and three collections of fi sh from the same pools in November 1995, May 1996, and August 1996. Re tention of fish appeared to be greater in pools with large woody debri s in May 1996. The presence of large woody debris in pools did not inf luence immigration or growth of cutthroat trout. However, both immigra tion and growth increased downstream over the 3850-m study reach. Low retention and substantial immigration of cutthroat trout into experime ntal pools indicate that movement is important in the dynamics of this population. First- and second-order channels appear to be important s ources of fish for the third-order study reach, while the study reach may export significant numbers of fish to downstream reaches accessibl e to anadromous fish.